Airbnb Mobile Engineer System Design Questions

Airbnb users often find themselves in areas with poor connectivity. Designing an offline-first synchronization engine ensures that user data is consistently synced and available, regardless of network conditions.
### Class: OfflineSyncEngine
- void saveData(String key, String value):
- Saves data locally when offline and queues it for synchronization.
- void syncData():
- Syncs queued data with the server once connectivity is regained.
- String getData(String key):
- Retrieves the requested data from local storage.### Example 1:
Input:
OfflineSyncEngine syncEngine = new OfflineSyncEngine()
syncEngine.saveData("booking_12345", "Booking details...")
syncEngine.syncData() when restored connectivity after going offline.
Output:
Data should be persistently stored and synced with the server.### Constraints:
- Each user may have up to 10,000 data entries.
- Sync operations should not exceed time limits of 2 seconds ideally, post connectivity restoration.

In Airbnb’s mobile application, users must receive real-time notifications about bookings, cancellations, messages, and promotions. Designing a robust notification system that seamlessly delivers these messages to users at scale is vital.### Class: NotificationManager
- void sendNotification(User user, String message):
- Sends a notification message to the specified user.
- List<Notification> getUserNotifications(User user):
- Returns a list of notifications for the specified user.
- void markAsRead(Notification notification):
- Marks the specified notification as read.
- List<Notification> getUnreadNotifications(User user):
- Retrieves all unread notifications for the specified user.### Example 1:
Input:
User user = new User(1, "Alice")
NotificationManager nm = new NotificationManager()
nm.sendNotification(user, "Your booking is confirmed!")
Output:
nm.getUserNotifications(user) returns List<Notification> containing the confirmation message.### Constraints:
- Users and notifications are uniquely identifiable.
- Each user can have up to 1,000 notifications.